1. Scope of the Invention
The present invention refers to a printed circuit board with insulated metal substrate with an integrated cooling system, said cooling system comprising one or more conduits for a heat-carrying fluid.
2. Technical Background
In printed circuit boards interconnecting electric and electronic power components, there is a drawback related to the dissipation or elimination of heat generated by such components. The use of dissipators or heat sinks is well known in the state of the art, which consist of elements of a highly heat conductive material thermally connected, either directly or indirectly, to the heat generating components or to a support substrate thereof and provided with a large surface area, frequently formed by fins, in contact with the circulating medium. Patents U.S. Pat. No. 5,875,097 and U.S. Pat. No. 6,219,246 disclose embodiment examples of such heat sinks, and patent U.S. Pat. No. 6,181,556 discloses an apparatus for electronic device heat dissipation composed of a combination of heat sinks provided with fins, arranged so as to encircle the component to be cooled and thermally connected together by means of thermal bridge elements, said heat sinks being submitted to an airflow generated by several fans.
The use of heat pipes is also known for keeping an electronic circuit component at a suitable working temperature. A heat pipe comprises a span of pipe closed on its ends and partially full of heat-carrying fluid, said pipe comprising at least one evaporation region located close to or in contact with the heat source and at least one condensation region, for example, exposed to the circulating air. Patent U.S. Pat No. 6,226,178 discloses a laptop computer in which a heat pipe has an evaporation region in contact with a heat generating microprocessor and two separate condensation regions connected to several respective different heat dissipating devices, one of them consisting of a heat sink with forced ventilation and the other consisting of an extensive passive heat dissipation board located behind the display. A drawback of this system is that the evaporation region is in contact with the single component or with an auxiliary board on which the component is assembled, but it does not cool the entire printed circuit board on which a plurality of heat generating components are assembled.
Patent U.S. Pat. No. 6,212,071 uses several tracks of a heat conducting material embedded on the substrate of a conventional printed circuit board and thermally connected on one end to those areas or components of the board where heat is generated and, on the other end, on the edge of the substrate, to several external dissipators, such as a metal casing encircling the board. These heat conducting tracks can be formed in a manner that is analogous to the electro-conducting tracks on a multi-layer board, in which case they would be of copper. They can also be formed by drilling several holes from the edge of the board and filling said holes with a melted metallic material, such as welding material. However, both the copper tracks or channels and those of the welding material are costly to manufacture and they have a relatively low heat dissipation yield. Said patent U.S. Pat. No. 6,212,071 suggests that conventional heat pipes can be used, but no construction or assembly details are given, no illustration on the arrangement thereof is claimed or provided.
Patents U.S. Pat. No. 6,190,941, U.S. Pat. No. 6,032,355 and U.S. Pat. No. 6,201,300 disclose various other forms of providing heat conduction paths through a substrate on a printed circuit board for dissipating heat generated by several components.
A technology that gives way to providing a high degree of heat dissipation to the support board of the components of a circuit is the printed circuit board with insulated metal substrate technology, commonly referred to in the sector as IMS. A typical printed circuit board with insulated metal substrate comprises at least one metal support substrate, generally of an aluminum alloy, on which the electro-conducting circuit tracks, generally copper, are adhered by means of a layer of electrically insulating material which is the best possible heat conductor. With this arrangement, part of the heat generated by the components is dissipated through the metal substrate, which acts like a heat sink. However, in power applications such as a control and distribution box in an automobile, the heat dissipation provided by the insulated metal substrate technology is not enough to ensure that a deterioration or malfunction of the circuit does not occur due to thermal fatigue.
Work has recently been done for improving effectiveness in terms of heat dissipation on printed circuit boards with insulated metal substrate. Patent U.S. Pat. No. 6,201,701 discloses a multi-layer structure of power and control component connection tracks, assembled on a thick insulated metal substrate. The multiple electro-conducting layers are separated by layers of electrically insulating material and between them heat communication paths are arranged which improve the heat dissipation efficiency. However, heat transmission is produced from the components and the electro-conducting tracks to the metal substrate, but no improvements are provided in terms heat evacuation from the metal substrate.
Therefore, there is still a need for a more effective, compact and economical cooling system for effectively dissipating the heat generated by electronic components, especially components submitted to intense regimens, printed circuit boards with insulated metal substrate in power applications, such as a control and distribution box in an automotive vehicle.